The invention relates to a twin-clutch transmission, in particular for a motor vehicle.
A twin-clutch transmission which comprises a first clutch and a second clutch which are arranged coaxially with one another and accordingly have a common axis of rotation is known from U.S. Pat. No. 6,499,370, for example. The twin-clutch furthermore comprises a first input shaft and a second input shaft. The first input shaft can be connected to an engine via the first clutch. The second input shaft can be connected to the engine via the second clutch.
A torque can be transmitted from the input shafts to an output shaft via a number of engageable gearwheel pairs. In this connection, a gearwheel pair consists of a fixed wheel and a loose wheel. The loose wheel is in each case assigned a gear-shifting clutch by means of which the loose wheel can be connected in a rotationally fixed manner to the shaft on which the loose wheel is arranged. With the gear-shifting clutch closed, the gearwheel pair transmits a torque from one of the input shafts to the output shaft.
In order to make possible a serial and/or parallel hybrid mode of the twin-clutch transmission, the twin-clutch transmission of U.S. Pat. No. 6,499,370 has a first drive unit and a second drive unit. In this connection, the two drive units are each designed as electric machines which are arranged coaxially with the two clutches and coaxially with the two input shafts.
Owing to the coaxial arrangement of the two clutches and of the two input shafts with the fixed wheels/loose wheels including gear-shifting clutches arranged thereon, and also owing to the electric machines arranged coaxially therewith, the twin-clutch transmission has a comparatively great overall axial length. This can lead to problems on installation in a motor vehicle with a given space availability. The space availability inside the engine space of the motor vehicle is very limited in particular when the twin-clutch transmission is to be mounted together with the engine transversely to the direction of travel. The problem of limited space availability is becoming more serious as a trend toward increasing the number of forward gears can be observed as far as manual transmissions are concerned. As a rule, an additional forward gear means a further gearwheel which is arranged on one of the input shafts and further increases the overall axial length.
A twin-clutch transmission with only one electric machine which can be switched to the first or the second input shaft as required by a switch-over device is known from DE 198 50 549. It is true that it is possible to dispense with one electric machine by virtue of such a switch-over device, but, in comparison with a twin-clutch transmission with two electric machines of which the parallel operation is provided at maximum load, for example, this individual electric machine has to be dimensioned to be larger in order to provide power corresponding to the sum of the individual powers of the two electric machines. However, an electric machine of such a size can also lead to packing problems again.